The present invention relates to the balancing of rotors, and more particularly to rotor balancing which compensates for position inaccuracies.
The invention is concerned with a method for taking into account position inaccuracies of attachment surfaces on rotors, which surfaces facilitate the later attachment of other components which possess mass, with respect to the ideal position of such surfaces on the rotor especially during balancing when only the unoccupied attachment surfaces are present, especially crankpins of crankshafts.
In order to simulate the partial mass of the crank mechanism that is later attached to each individual crankpin, such crank mechanism consisting of connecting rod, piston, piston rings, and wristpin, unbalance compensation masses in the form of bob weights of annular shape are clamped to each crankpin. If in this case there is a deviation in the position of the crankpins from their ideal position on the crankshaft, then the bob weights take this deviation into account. Such deviation may, for example, occur in a V-8 engine in a form that the angular spacing of the individual crankpin axes to each other is no longer 90.degree. but has a different value. The same is true for the radial distance of the crankpin axes from the axis of the crankshaft. These deviations are also taken care of by the bob weights and will no longer have any effect when the total crank mechanism has been assembled.
Attaching and detaching of such bob weights before and after unbalance measurements in the crankshaft is very time consuming. Therefore, balancing machines were equipped with compensating masses (bob weight eliminators) which take into account the influences of the eccentric position of the crankpins on the crankshaft and which are located remote from the crankshaft on the headstock spindle which drives the crankshaft. These compensating masses are arranged at appropriate angular spacing toward each other and at the appropriate radial distance from the axis of the drive spindle in order to eliminate the existing unbalance. Such compensating masses are determined according to nominal dimensions such as the ideal values of angular spacing and radial distance of the individual crankpins. In cases where the crankpins are arranged in symmetry, attachment of bob weights or the use of compensating masses is not necessary since the effect of the ideal values is self compensating based upon the symmetry. If a crankshaft thus compensated rotates, a balance error is necessarily created because of the deviation of the actual from the ideal or "nominal" values of the crankshaft. When the remainder of the crank mechanisms are later connected to the crankshaft, a detrimental effect results. This balance error may exceed the balance tolerance.
The above is true not only for crankshafts but for any rotor with attachment surfaces arranged in prescribed geometric position to the axis of rotation and in prescribed geometric position to each other and arranged on the circumference of a basic body. These surfaces facilitate the later attachment of other components, and as a result of manufacturing tolerances, they often deviate from the geometrically prescribed theoretical position.